Donald Trump in the White House

Secretary of State Tillerson was restrained as he addressed the operation.

"We are concerned about the Turkish incident in northern Syria," he said during a joint press conference in London with British foreign secretary Boris Johnson. "We recognize and fully appreciate Turkey's legitimate right to protect its own citizens from terrorist elements."

Turkish foreign minister Mevlüt Çavusoglu was quoted by online news outlet Arti Gercek saying that the two leaders will speak on Wednesday.